Ch.16 - Aqueous Equilibrium See all chapters
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Ch.1 - Intro to General Chemistry
Ch.2 - Atoms & Elements
Ch.3 - Chemical Reactions
BONUS: Lab Techniques and Procedures
BONUS: Mathematical Operations and Functions
Ch.4 - Chemical Quantities & Aqueous Reactions
Ch.5 - Gases
Ch.6 - Thermochemistry
Ch.7 - Quantum Mechanics
Ch.8 - Periodic Properties of the Elements
Ch.9 - Bonding & Molecular Structure
Ch.10 - Molecular Shapes & Valence Bond Theory
Ch.11 - Liquids, Solids & Intermolecular Forces
Ch.12 - Solutions
Ch.13 - Chemical Kinetics
Ch.14 - Chemical Equilibrium
Ch.15 - Acid and Base Equilibrium
Ch.16 - Aqueous Equilibrium
Ch. 17 - Chemical Thermodynamics
Ch.18 - Electrochemistry
Ch.19 - Nuclear Chemistry
Ch.20 - Organic Chemistry
Ch.22 - Chemistry of the Nonmetals
Ch.23 - Transition Metals and Coordination Compounds
Identifying a Buffer

A buffer is a solution composed of a weak acid with its conjugate base. 

Concept #1: Understanding a Buffer.

Buffers resist drastic changes to the pH if a strong acid or strong base is added. 

If a strong base is added then the buffer resists a pH change by having the weak acid neutralize it. 

If a strong acid is added then the buffer resists a pH change by having the conjugate base neutralize it. 

Practice: Which one of the following combinations does not create a buffer?

Practice: Which of the following combinations can result in the formation of a buffer?

Buffer Creation

As we stated earlier a buffer is composed of a weak acid and its conjugate base, but there are actually three ways to create a buffer.

Concept #2: Method 1 for  Creating a Buffer. 

The first and most obvious way to create a buffer is to simply combine a weak acid and its conjugate base. In this case, a buffer is most ideal when both components are highly concentrated and equal to one another. 

The weak acid and conjugate base can be different from one another by up to a magnitude of 10. This is called the buffer range. If they are different by more than 10 then this is considered a bad buffer.

Concept #3: Method 2 for Creating a Buffer. 

The second method in creating a buffer is mixing a strong acid with a weak base. In this case since we have a strong species mixing with a weak species then we must make sure the weak species is higher in amount. 

Concept #4: Method 3 for  Creating a Buffer.

The third method in creating a buffer is mixing a strong base with a weak acid. In this case since we have a strong species mixing with a weak species then we must make sure the weak species is higher in amount. 

Example #1: Which of the following combinations can result in the formation of a buffer?

a)     0.01 moles HClO (hypochlorous acid) and 0.05 moles of NaOH.

b)     0.01 moles HClO (hypochlorous acid) and 0.05 moles of HCl.

c)     0.01 moles HClO (hypochlorous acid) and 0.05 moles of NH3.

d)     0.01 moles HClO (hypochlorous acid) and 0.001 moles of NaOH

Practice:  Which of the following combinations can result in the formation of a buffer?

Practice: A buffer solution is comprised of 50.0 mL of a 0.100 M HC2H3O2 and 60.0 mL of a 0.100 M NaC2H3O2. Which of the following actions would completely destroy the buffer?

Henderson – Hasselbalch Equation

Concept #5: The Henderson – Hasselbalch Equation.

Whenever we have a buffer we can skip the ICE Chart and use the Henderson Hasselbalch. 

Example #2: What is the pH of a solution consisting of 2.75 M sodium phenolate (C6H5ONa) and 3.0 M phenol (C6H5OH). The Ka of phenol is 1.0 x 10-10

Practice: Calculate the pH of a solution formed by mixing 200 mL of a 0.400 M C2H5NH2 solution with 350 mL of a 0.450 M C2H5NH3solution. (Kb of C2H5NHis 5.6 x 10 -4).

Example #3: What is the buffer component concentration ratio, [Pr ] / [HPr] , of a buffer that has a pH of 5.11. (The Ka of HPr is 1.30 x 10-5). 

Example #4: Over what pH range will an oxalic acid (H2C2O4) / sodium oxalate (NaHC2O4) solution work most effectively? The acid dissociation constant of oxalic acid is 6.0 x 10-2.

a) 0.22 – 2.22        b) 1.00 – 3.00        c) 0.22 – 1.22        d) 2.0 – 4.0

Practice: Determine how many grams of sodium acetate, NaCH3CO2 (MW: 82.05 g/mol), you would mix into enough 0.065 M acetic acid CH3CO2H (MW: 60.05 g/mol) to prepare 3.2 L of a buffer with a pH of 4.58. The Ka is 1.8 x 10-5.

Example #5: Which weak acid-conjugate base combination would be ideal to form a buffer with a pH of 4.74.

a)     Cyanic acid and Potassium cynate           (Ka = 4.9 x 10-10)

b)     Benzoic acid and Lithium benzoate         (Ka = 6.3 x 10-5)

c)     Acetic acid and Sodium acetate                   (Ka = 1.7 x 10-5)

d)     Ammonium chloride and Ammonia         (Ka = 5.56 x 10-10)

e)     Formic acid and Cesium formate                (Ka = 1.7 x 10-4)

Practice: A buffer solution is made by combining a weak acid with its conjugate salt. What will happen to the pH if the solution is diluted to one-fourth of its original concentration?

Additional Problems
What is the pH of a buffer solution that contains 0.55 M methylamine, CH 3NH2, and 0.29 M of methylammonium chloride, CH3NH3Cl? A. 3.63 B. 10.32 C. 10.92 D. 10.37 E. 3.08
Which pair of substance can be dissolved together (in the right ratio) to prepare a buffer solution? i, C2H3O2H ii. NaC2H3O2 iii. NaOH iv. HCl v. NaCl A. i and ii B. i and iii C. ii and iii D. i and ii, ii and iv, i and iii E. iv and v; i and iii
Calculate the pH of a solution made by mixing 8.627 g of sodium butanoate in enough 0.452 M butanoic acid, HC4H7O2 , to make 250.0 mL of solution. A. 4.75 B. 4.82 C. 5.00 D. 2.58 E. 4.65
Which of the following solutions is a good buffer system? A) A solution that is 0.10 M HC2H3O2 and 0.10 M LiC2H3O2 B) A solution that is 0.10 M HBr and 0.10 M KC 2H3O2 C) A solution that is 0.10 M HI and 0.10 M NH 4+ D) A solution that is 0.10 M NaOH and 0.10 M KOH E) None of the above are buffer systems.
If a biochemist wishes to prepare a buffer that will be effective at a pH of 3.0 (at 25°C) for studying peptide degradation, what will be the best choice for the acid component? (a) Oxalic acid (H2C2O4), Ka = 5.9 x 10 -2 (b) Hydrofluoric acid (HF), Ka = 6.6 x 10 -4 (c) Pyridinium ion (HC5H5N+ ), Ka = 5.6 x 10 -6 (d) Hypochlorous acid (HClO), Ka = 3.0 x 10 -8 (e) Hydrocyanic acid (HCN), Ka = 6.17 x 10 -10 
How much sodium lactate NaC3H3O3, should be added to 583.58 mL of a 0.473 M lactic acid, HC3H3O3, solution to make a buffer of pH 4.08? (assume any change in volume is insignificant and that  the pKa is rounded to two significant figures) a. 6.986 grams b. 1.157 grams c. 127.4 grams d. 17.89 grams e. 51.59 grams
Which one of the following pairs of substances cannot be mixed together (in any quantities) to form a buffer solution? (a) H3PO4, KH2PO4 (b) NH3, NH4Cl (c) HNO2, NaNO2 (d) CH3COONa, CH3COOHa (e) HNO3, KOH  
The Henderson–Hasselbalch (H-H) equation is a clever rearrangement of the  Ka equilibrium expression that comes in very handy for certain pH calculations. The H-H equation can be used to calculate the buffer ratio ([base]/[acid]) required to prepare a buffer at a specific pH. It is possible that the buffer ratio required to prepare a pH 6.85 buffer could be used to study novel chemotherapy agents; however, the noble H-H equation can be used for more nefarious purposes.
Which of the following weak acids would be BEST to use to make a buffer of pH = 2.90 a. lactic b. butanoic c. chloroacetic d. benzoic e. hypochlorous
Which of the following weak acids would be BEST to use to make a buffer of pH = 3.52? a. nitrous acid b. hydrofluoric acid c. chloroacetic acid d. lactic acid e. benzoic acid
You add a small amount of HCl to a solution of 0.20 M HBrO and 0.20 M NaBrO. What do you expect to happen? 1. The [OH−] will decrease slightly. 2. The H+ ions will react with the HBrO molecules. 3. The pH will increase slightly. 4. The Ka for HBrO will increase. 
The pH of a sodium acetate-acetic acid buffer is 4.50. Calculate the ratio of [CH3COO- ]/[CH3COOH].
Consider a buffer composed of a mixture of acetic acid and sodium acetate in equal amounts. Which of the following clearly indicates what happens to the buffer when a very small amount of concentrated LiOH is added to it.    [CH3COOH]      [CH 3COO – ]          pH A. increases          decreases        decreases B. decreases         increases          increases C. increases          decreases         increases D. decreases         increases          decreases E. increases          increases           increases
A solution contains 1.00 mole of acetic acid and has pH = 2.50. How many grams of NaCH3COO·3H2O (of MW 136) should be dissolved in the solution to raise the pH to 4.00? 1. 10 g 2. 35 g 3. 20 g 4. 15 g 5. 24 g
Which one of the following combinations CANNOT function as a buffer solution? A)        H2C2O4 and CsHC2O4             D)       HF and LiF B)        NH3 and (NH4)2SO4                 E)        HCl and NaCl C)        K2HPO4 and KH2PO4             
Calculate the pH of a buffer solution that contains 0.25 M chloroacetic acid (ClCH2CO2H) and 0.15 M sodium chloroacetate (ClCH2CO2Na).  [Ka = 1.4 × 10–3  for chloroacetic acid] A)  3.07    B)  2.85    C)  4.19    D)  2.63    E)  4.41
You are asked to go into the lab and prepare a buffer solution with a pH of 6.40 ± 0.2.  Which weak acid would be the best choice?             A)  carbonic acid                                Ka = 4.2 x 10-7                B)  phenol                                           Ka = 1.3 x 10-10                C)  ascorbic acid                                 Ka = 8.0 x 10-5                D)  hydrosulfuric acid                          Ka = 9.5 x 10-8                E)  potassium hydrogen phthalate      Ka = 3.1 x 10-6    
Explain why the salt of a weak acid, as well as the acid itself, must be present to form a buffer solution. 1. The anion from the salt is needed to partially neutralize added base. 2. The anion from the salt is needed to partially neutralize added acid. 3. The cation from the salt is needed to partially neutralize added acid. 4. The cation from the salt is needed to partially neutralize added base. 5. Actually, a weak acid by itself is a buffer; no salt is needed. 
Identify a good buffer. A) small amounts of both a weak acid and its conjugate base B) significant amounts of both a strong acid and a strong base C) small amounts of both a strong acid and a strong base D) significant amount of both a weak acid and a strong acid E) significant amounts of both a weak acid and its conjugate base
A student is asked to prepare a buffer solution at pH = 8.60 using one of the following weak acids: HA (Ka = 2.7 x 10-3), HB(Ka= 4.4x10-6), HC (Ka = 2.6 x 10-9), Which acid should she choose?
You wish to prepare an HC 2H3O2 buffer with a pH of 4.24. If the pK a of is 4.74, what ratio of C2H3O2- / HC2H3O2 must you use? A) 0.10 B) 0.50 C) 0.32 D) 2.0 E) 2.8
Blood contains a buffer of carbonic acid (H2CO3) and hydrogen carbonate ion (HCO3-) that keeps the pH at a relatively stable 7.40. What is the ratio of [HCO3-] / [H2CO3] in blood? Ka1 = 4.30x10-7 for H2CO3.  0.0926 10.8 3.98 x 10-8 1.71 x 10-14
One liter of a buffer from the blood is found to have 0.4 moles of acid (pK a = 4.76) and 0.1 moles of conjugate base. a. Is this pH of buffer greater than, equal to, or less than 4.76? Show your reasoning mathematically?   b. You want to get the buffer to maximum buffering capacity. You have HCl and NaOH available. Which would you add and how much in terms of moles? c. Is the pH of the buffer after step b greater than, equal to, or less than to 4.76?    
What is the effective pH range of the pyridine/pyridinium chloride buffer? For pyridine, the value of Kb is 1.8 x 10-9. (a) 9.1-11.1 (b) 1.4-3.4 (c) 10.3-12.3 (d) 7.7-9.7 (e) 4.3-6.3  
A solution was made by dissolving 0.1219 moles of sodium acetate in 200.0 mL of  1.00 M acetic acid.  Assuming the change in volume when the sodium acetate is not significant, estimate the pH of the solution. The Ka for acetic acid is 1.7 x 10-5.    A.  5.42   B.  7.31   C.  9.42   D.  4.56   E.  2.89
Which of the following procedures will result in the largest change in pH? Adding NaNO2 to a solution of HNO2 in water or  Adding NaNO3 to a solution of HNO3 in water  
The addition of hydrochloric acid and __________ to water produces a buffer solution. a. HC6H5O   b. NaOH c. NH3 d. HNO3 e. NaNO3
Which one of the following pairs, when mixed, do not form a buffered solution? a) 1.0 M CH3CH2NH2/1.0 M CH3CH2NH3Cl b) 1.0 M CH3CH2COOH/1.0 M CH3CH2COONa c) 1.0 M KOH/1.0 M HI d) 1.0 M NH3/1.0 M NH4Cl e) 1.0 M H3PO4/1.0 M KH2PO4
A buffer solution is made by combining a weak acid with its conjugate salt. What will happen to the pH if the solution is diluted to one-half of its original concentration? a) The pH will increase. b) The pH will decrease. c) The pH will remain constant. d) The solution will become more neutral. 
Which weak acid-conjugate base combination would be the best to create a solution with a pH of 4.193?      a)  Butanoic acid and Potassium butanoate (Ka = 1.5 x 10-5)      b)  Benzoic acid and Sodium benzoate (Ka = 6.3 x 10-5)      c)  Acetic acid and Lithium acetate (Ka = 1.8 x 10-5)      d)  Ammonium chloride and Ammonia (Kb = 1.8 x 10-5)      e)  Hypochlorous acid and sodium hypochlorite (Ka = 2.9 x 10-8)
Over what pH range will an oxalic acid (H 2C2O4) / sodium oxalate (NaHC2O4) solution work most effectively? The acid dissociation constant of oxalic acid is 6.0 x 10-2. a) 0.22 – 2.22                 b) 1.00 – 3.00                  c) 0.22 – 1.22                   d) 2.0 – 4.0
What is the pH of a solution which is 0.400 M in dimethylamine (CH 3)2NH) and 0.600 M in dimethylamine hydrochloride (CH3)2NH2+Cl−)? Kb for dimethylamine = 0.00074. 1. 10.78 2. 2.95 3. 10.87 4. 3.31 5. 10.69  6. 11.05 7. 11.21
Find the pH of a buffer solution made by mixing 100 mL of 0.20 M methylamine, CH3NH2, with 250.0 mL of a 0.50 M CH  3NH3Cl. Kb of methylamine is 4.4 x 10-4.   
How many moles of solid NaF would have to be added to 1.0 L of 1.90   M HF solution to achieve a pH of 3.35? Assume there is no volume change. (Ka for HF = 7.2 x 10 -4)       
Which of the following buffer systems would you use to create a buffer with a pH of 4.0? The Ka of nitrous acid, HNO2 is 4.5 x 10-4. a) 0.30 M HNO2 / 0.22 M NaNO2 b) 0.22 M HNO2 / 0.30 M NaNO2 c) 0.11 M HNO2 / 0.50 M NaNO2 d) 0.50 M HNO2 / 0.11 M NaNO2 e) 0.30 M HNO2 / 0.30 M NaNO2
To create a buffer that maintains a pH around 7.54, which solution would you choose? A. CH3COOH and NaCH3COO B. HClO and KClO C. NaOH and HCN D. HNO3 and KNO3
Calculate the pH of a buffer that is 0.225 M HC 2H3O2 and 0.162 M KC2H3O2. The Ka for HC2H3O2 is 1.8 × 10-5.  A) 4.89 B) 9.11 C) 4.74 D) 9.26 E) 4.60
Which of the following is TRUE? A) An effective buffer has a [base]/[acid] ratio in the range of 10 - 100. B) A buffer is most resistant to pH change when [acid] = [conjugate base] C) An effective buffer has very small absolute concentrations of acid and conjugate base. D) A buffer can not be destroyed by adding too much strong base. It can only be  destroyed by adding too much strong acid. E) None of the above are true.  
Which of the following solutions is a good buffer system? A) A solution that is 0.10 M NaCl and 0.10 M HCl B) A solution that is 0.10 M HCN and 0.10 M LiCN C) A solution that is 0.10 M NaOH and 0.10 M HNO 3 D) A solution that is 0.10 M HNO3 and 0.10 M NaNO 3 E) A solution that is 0.10 M HCN and 0.10 M KI
Which of the following acids and their conjugate base would form a buffer with a pH of 8.10?   A. HClO3 pKa= 7.54 B. H2SO3 pKa= 1.77 C. HC2H3O2 pKa= 4.74 D. HNO2 pKa= 3.34 E. HIO pKa= 10.64
When to use the Henderson-Hasselbalch Equation Anytime we have a buffer we use it. Buffer  =  Weak Acid  &  Conjugate Base        OR          Conjugate Acid   &  Weak Base A buffer can be destroyed by adding ____________ or ____________.     There are 3 ways to form a buffer: Mixing a WEAK acid and its CONJUGATE base. An ideal buffer, in this case, is when both are equal in amount. An ideal buffer happens at the half-equivalence point. EX: _______________ HF  and _______________ NaF                 2. Mixing a  STRONG acid and a  WEAK base. In this case, the  WEAK base must be higher in amount than the  STRONG acid.           EX:  _______________ HCl and  _______________ CH3NH2         3. Mixing a  WEAK acid and a  STRONG base. In this case, the  WEAK acid must be higher in amount than the  STRONG base.               EX:    _______________ HNO2  and  _______________ NaOH
Which of the following acids and their conjugate base would form a buffer with pH of 3.34? HClO Ka = 2.9 x 10 –8 C6H5CO2H Ka = 6.5 x 10 –5 HF Ka = 3.5 x 10 –4 HIO3 Ka = 1.7 x 10 –1 HClO2 Ka = 1.1 x 10 –2
A buffer is prepared using 0.085M formic acid and 0.085M sodium formate. Which of the following statements is false?  
An aqueous solution contains 0.26M hydrocyanic acid, HCN. One liter of this solution could be converted to a buffer by the addition of:    
What is the pH of a solution of 0.46 M acid and 0.36 M of its conjugate base if the pKa is 5.51? a) 4.70 b) 4.90 c) 5.20 d) 5.40 e) 5.62
Determine how many grams of potassium hypochlorite, KClO (MW: 90.55 ), you would mix into enough 0.055 M hypochlorous acid, HClO (MW: 52.46 ) to prepare 5.0 L of a buffer with a pH = 6.77. Ka of HClO is 2.9 x 10-8.
A buffer: a. can be made by a combination of a strong acid and strong base. b. can be a combination of a weak acid and its conjugate base. c. resists changes in pH. d. both A and C e. both B and C
A buffer solution is comprised of 50.0 mL of a 0.100 M HC 2H3O2 and 60.0 mL of a 0.100 M NaC2H3O2. Which of the following actions would completely destroy the buffer? a) Adding 0.003 mol HC2H3O2 b) Adding 0.007 mol Ca(C2H3O2)2 c) Adding 0.005 mol NaH d) Adding 0.004 mol HNO3
Which weak acid-conjugate base combination would be the best to create a solution with a pH of 7.538? a) Butanoic acid and Potassium butanoate (Ka = 1.5 x 10 -5) b) Benzoic acid and Sodium benzoate (Ka = 6.3 x 10 -5) c) Acetic acid and Lithium acetate (Ka = 1.8 x 10 -5) d) Ammonium chloride and Ammonia (Kb = 1.8 x 10 -5) e) Hypochlorous acid and sodium hypochlorite (Ka = 2.9 x 10 -8)
Which of the following is TRUE? a) An effective buffer has a [base]/[acid] ratio in the range of 10 - 100. b) A buffer is most resistant to pH change when [weak acid] = [conjugate base] c) An effective buffer has very small absolute concentrations of weak acid and conjugate base. d) A buffer cannot be destroyed by adding too much strong base, it can only be destroyed by adding too much strong acid.  e) None of the above are true.
Which of the following combinations can result in the formation of a buffer? a) HBr and NH4Cl b) LiOH and HNO3 c) H3PO4 and LiH2PO4 e) None of these combinations result in a buffer.
To create a buffer that maintains a pH around 7.54, which solution would you choose? A. CH3COOH and NaCH3COO B. HClO and KClO C. NaOH and HCN D. HNO3 and KNO3
Which of the following combinations can result in the formation of a buffer? a) 90 mL of 0.10 M HCN with 70 mL of 0.10 M NH  3. b) 70 mL of 0.10 M HC 2H3O2 with 30.0 mL of 0.15 M Ba(OH) 2. c) 50 mL of 0.10 M HNO3 with 50 mL of 0.10 M NaOH. d) 70 mL of 0.10 M HNO2 with 25 mL of 0.10 M LiH. e) 70 mL of 0.10 M HClO with 70 mL of 0.10 M LiOH. 
What is the pH of a solution that is 0.2 M in acetic acid (Ka= 1.8 x 10  -5) and 0.2 M in sodium acetate? A. 4.7 B. 9.3 C. 7.0 D. 5.4 E. 8.6
Which of the following pairs of solution does not produce a buffer? A. 0.3 M HClO3 & 0.2 M KOH B. 0.2 M NH3 & 0.1 M HClO4 C. 1.5 M HF & 1 M LiOH D. 0.1 M KCOOH & 0.1 M NaCOOH
Consider a solution consisting of the following two buffer systems: H2CO3    ⇌ HCO3 - + H +          pKa = 6.4 H2PO4 -   ⇌ HPO4-2 + H +         pKa = 7.2 At pH 6.4, which one of the following is TRUE of the relative amounts of acid and conjugate base present? A) [H2CO3] = [HCO3 - ] and [H2PO4 - ] > [HPO4 -2 ] B) [H2CO3] > [HCO3 - ] and [H2PO4 - ] > [HPO4 -2 ] C) [H2CO3] = [HCO3 - ] and [HPO4 -2 ] > [H2PO4 - ] D) [HCO3 - ] > [H2CO3] and [HPO4 -2 ] > [H2PO4 - ]  E) [H2CO3] > [HCO3 - ] and [HPO4 -2] > [H2PO4 -]
How many moles of solid NaF would have to be added to 1.0 L of 1.90 M HF solution to achieve a buffer of pH 3.35? Assume there is no volume change. (Ka for HF = 7.2 x 10 -4) A. 3.1 B. 2.3 C. 1.6 D. 1.0 E. 4.9 
Calculate the pH of a buffer that is 0.145M in acetic acid and 0.202M in sodium acetate. The acid dissociation constant for acetic acid 1.75x10 –5. 4.60 4.89 5.05 4.74 9.01
Calculate the pH of a solution that is 0.210M in nitrous acid and 0.290M in potassium nitrite. The acid dissociation constant of nitrous acid is 4.50x10 –4. 3.21 3.49 13.86 10.51 4.56
Which of the following acids and their conjugate base would form a buffer with a pH of 8.10? HClO3 pKa = 7.54 H2SO3 pKa = 1.77 HC2H3O2 pKa = 4.74 HNO2 pKa = 3.34 HIO pKa = 10.64
Two compounds, HA & HB have the same K a value. If a solution is prepared containing 0.5  mole of HA and 0.5 of NaB which of the following is True? A) The solution pH = pKa but it has no Buffer Capacity B) The solution is not a Buffer because there is no conjugate base of A or conjugate acid of B-. C) This solution is a good Buffer because the [weak base] = [weak acid] D) The pH = pKb for the B- E)  It is not possible to determine if this is a good buffer or not.
Determine whether or not the mixing of each of the two solutions indicated below will result in a buffer:75.0 mL of 0.10M HF  55.0 mL of 0.15 M NaF
A 100.0 mL buffer solution is 0.175 M in HClO and 0.150 M in NaClO. What is the pH after addition of 0.090 g of NaOH?
Find the ratio of the volumes of NaC 3H5O3 soloution to HC3H5O3 (lactic acid) required to prepare a buffer with a pH of 3.90. The solutions are equal in molarity. Ka = 1.4x10-4 for HC3H5O3.
Calculate the pH of a buffer that is 0.225 M HC 2H3O2 and 0.162 M KC2H3O2. The Ka for HC2H3O2 is 1.8 × 10-5.
75.0 mL of 0.10 M HF; 55.0 mL of 0.15 M NaFa. this will be a bufferb. this will not be a buffer 
150.0 mL of 0.10 M HF; 135.0 mL of 0.175 M HCla. this will be a bufferb. this will not be a buffer
165.0 mL of 0.10 M HF; 135.0 mL of 0.050 M KOHa. this will be a bufferb. this will not be a buffer 
125.0 mL of 0.15 M CH3NH2; 120.0 mL of 0.25 M CH3NH3Cl a. this will be a bufferb. this will not be a buffer 
105.0 mL of 0.15 M CH3NH2; 95.0 mL of 0.10 M HCla. this will be a bufferb. this will not be a buffer 
Which pair of compounds will form a buffer in aqueous solution? A. HCl and NaOH B. NaCN and KCN C. HCN and HCl D. HCN and NaCN E. NaCN and NaOH F. HCl and NaCl
Which of the following solutions is a buffer?a. A solution made by mixing 100 mL of 0.100 M KClO and 50 mL of 0.100 M KCl.b. A solution made by mixing 100 mL of 0.100 M HClO and 500 mL of 0.100 M NaOH.c. A solution made by mixing 100 mL of 0.100 M HClO and 50 mL of 0.100 M NaOH.d. A solution made by mixing 100 mL of 0.100 M HClO and 50 mL of 0.100 M HCl.
Benzoic acid (C7H6O2) is a weak acid whose Ka is 6.5 x 10-5. If 0.490 g of benzoic acid are dissolved in 250 ml of water what mass of sodium benzoate (NaC7H5O2) would need to be added to adjust the pH of of the solution to 5.20? (You may assume that the added sodium benzoate doesn't significantly change the solution volume).
A buffer contains significant amounts of acetic acid and sodium acetate.a. Write a molecular equation showing how this buffer neutralizes added acid HNO 3.b. Write a molecular equation showing how this buffer neutralizes added base KOH.
Which set of compounds would form a buffer in aqueous solution?HBr and NaBrHCl and HClONaF and KFHF and KFNaF and NaOHNaCl and KClHCN and NaCN
Complete the following chemical equations to show what happens when HBr or KOH is added to a buffer solution made from HF and KF. List the products in alphabetical order within each reaction.
CN- is the conjugate base to the weak acid HCN, with K a = 6.0 x 10 -10, pKa = 9.22.Given a 50mL of a 0.1 M of NaCN (which dissociates completely), how many mL of 1.0 M HCl should be added to the solution in order to to bring the pH to 9.22?
How does a buffer resist change in pH upon addition of a strong acid? a) The strong acid reacts with the weak base in the buffer to form a weak acid, which produces few H+ ions in solution and therefore only a little change in pH. b) The strong acid reacts with the weak acid in the buffer to form a weak base, which produces few H+ ions in solution and therefore only a little change in pH. c) The strong acid reacts with the strong base in the buffer to form a salt which, produces few H  + ions in solution and therefore only a little change in pH.
How could you make a buffer? Select all that apply. a) Partially neutralize a weak base solution by addition of a strong acid. b) Add appropriate quantities of weak acid and its conjugate base to water. c) Partially neutralize a strong acid solution by addition of a strong base. d) Partially neutralize a weak acid solution by addition of a strong base. e) Partially neutralize a strong base solution by addition of a strong acid.
Complete this table of initial and final concentrations.              HF(aq) + KOH(aq) → KF(aq) + H  2O(l)Initial:    2.0 M      1.0M            0MFinal:Which of the following best describes the final solution?a. a neutral salt solutionb. a bufferc. none of the above
What mass of solid NaCH3CO2 (molar mass=82.0 g/mol) should be added to 1.0 L of 0.50 M CH3CO2H to make a buffer with a pH of 7.21? (pKa of CH 3CO2​H = 7.21)  
Which of the following solutions is a good buffer system?a. A solution that is 0.10 M HC2H3O2 and 0.10 M LiC2H3O2b. A solution that is 0.10 M HF and 0.10 M NaC 2H3O2c. A solution that is 0.10 M NaOH and 0.10 M KOHd. A solution that is 0.10 M HCl and 0.10 M NH 4+e. None of the above are buffer systems
a) Calculate the percent ionization of a 0.16M benzoic acid solution in pure water.b) Calculate the percent ionization of a 0.16M benzoic acid solution in a solution containing 0.11M sodium benzoate.
Which one of the following pairs cannot be mixed together to form a buffer solution? Why?a. NH3, NH4Clb. NaC2H3O2, HCl (C2H3O2- = acetate)c. RbOH, HBrd. KOH, HFe. H3PO4, KH2PO4
The addition of hydrofluoric acid and __________ to water produces a buffer solution. Why / how?a. HClb. NaNO3c. NaFd. NaCle. NaBr
Which of the following solutions could be classified as a buffer?a. 0.100 M HCl and 0.100 M NH4Clb. 0.100 M HBr and 0.100 M KBrc. 0.100 M HNO2 and 0.100 M NaNO2d. 0.100 M HCl and 0.100 M NaOH 
Which of the following buffer systems would be the best choice to create a buffer with pH = 9.05? a. HF / KFb. HNO2 / KNO2c. NH3 / NH4Cld. HClO / KClO
What mass of ammonium chloride, NH 4Cl, (Ka = 5.6 x 10 -10) must be added to exactly 500mL of 0.10M NH3 solution to give a solution with a pH of 9.00?
What is the pH of a solution prepared by mixing 0.250 mol of benzoic acid (C6H5COOH, Ka=6.50 x 10 –5) and 0.150 mol of sodium benzoate (C6H5COONa) in sufficient water to yield a 1.00 L solution? a) 3.965 b) 4.190 c) 4.411 d) 7.321 e) 10.084
What mass of ammonium chloride (NH 4Cl, molar mass 53.5g/mol) must be added to a 0.500mL solution of 0.250M ammonia to make a buffer with a pH of 9.26?
At a pH of 7.40, what is the ratio of the molar concentrations of PO 43− to HPO42−?Express your answer using two significant figures.
Which of the following solutions is a buffer? Check all that apply.a. A solution made by mixing 100 mL of 0.100 M HCOOH and 500 mL of 0.100 M NaOH.b. A solution made by mixing 100 mL of 0.100 M HCOOH and 50 mL of 0.100 M NaOH.c. A solution made by mixing 100 mL of 0.100 M HCOOK and 50 mL of 0.100 M KCl.d. A solution made by mixing 100 mL of 0.100 M HCOOH and 50 mL of 0.100 M HCl.
At a pH of 7.40, what is the ratio of the molar concentrations of H 2PO4− to H3PO4?Express your answer using two significant figures.
Which pair of compounds will form a buffer in aqueous solution? a. HCN and NaCN b. HCl and NaOH c. NaCN and NaOH d. HCN and HCl e. HCl and NaCl f. NaCN and KCN
Which solution has the greatest ability to resist a change in pH (or buffering capacity)? a) 0.543 M NH3 and 0.555 M NH4 Clb) 0.087 M NH3 and 0.088 M NH4 Clc) 0.234 M NH3 and 0.100 M NH4 Cld) 0.100 M NH3 and 0.455 M NH4 Cle) They are all buffer solutions and would all have the same capacity.
The addition of hydrochloric acid and __________ to water produces a buffer solution.a) HC6H5Ob) NaOHc) NH3d) HNO3e) NaNO3
At a pH of 7.40, what is the ratio of the molar concentrations of CO  32− to HCO3−?Express your answer using two significant figures.
At a pH of 7.40, what is the ratio of the molar concentrations of HCO  3− to H2CO3?Express your answer using two significant figures.
The Ka values for nitrous acid (HNO2) and hypochlorous (HCIO) acid are 4.5 x 10 -4 and 3.0 x 10 -8 respectively.What other substance containing sodium would be needed to make the buffer? Express your answer as a chemical formula.
A certain aqueous HCNO solution has a pH of 2.17. If solid KCNO is added to the solution, will the pH increase, decrease, or remain the same? Assume that there is no volume change upon addition of KCNO.
Nitric acid, HNO2 is a weak acid with Ka= 4.5 x 10-4. It dissociates according to: HNO2 (aq) ⇌ H+(aq) + NO2-(aq) a.) What is the pH of a buffer solution which is 0.80 M in NO2- and 0.40 M in HNO2?     b.) What will be the pH of the resulting solution when 2.0 mL of 0.5 M HCl are added to 50 mL of this (from part a) buffer solution?       c.) What will be the pH of the resulting solution when 2.0 mL of 0.5 M NaOH are added to 50 mL of this (from part a) buffer solution?
Which pair of compounds will form a buffer in aqueous solution? a. NaCN and NaOH b. NaCN and KCN c. HCl and NaOH d. HCN and NaCN e. HCN and HCl f. HCl and NaCl
Of the following, which is the best base to create a buffer with a pH = 8.0?a. Aniline, Kb = 4.3 x 10-10b. Ethylamine, Kb = 6.4 x 10-4c. Hydrazine, Kb = 1.3 x 10-6d. Pyridine, Kb = 1.7 x 10-9
Which pair of compounds will form a buffer in aqueous solution? a. HCl and NaOH b. NaCN and KCN c. HCN and HCl d. HCN and NaCN  e. NaCN and NaOH
Which of the following molar ratios is the correct equilibrium ratio of BASE: ACID for a solution made of aniline (Kb = 3.8 x 10-10) and anilinum nitrate where the pH is 4.80? 1. 1:2 2. 3:5 3. 7:2 4. 2:1 5. 5:3 6. 4:1 7. 9:1
Of the following solutions, which has the greatest buffering capacity?a. 0.296 M HF and 0.122 M NaFb. 0.195 M HF and 8.02 x 10−2 M NaFc. 0.591 M HF and 0.243 M NaFd. 1.18 M HF and 0.486 M NaFe. They are all buffer solutions and would all have the same capacity.
Of the following solutions, which has the greatest buffering capacity?a. 0.100 M NH3 and 0.455 M NH4CIb. 0.087 M NH3 and 0.088 M NH4CIc. They are all buffer solutions and would all have the same capacity.d. 0.234 M NH3 and 0.100 M NH4CIe. 0.543 M NH3 and 0.555 M NH4CI
The Ka of acetic acid is 1.8 x 10-5 at 25°C. a) What is the pH of a 0.5 M solution of acetic acid at 25°C? b)What is the pH of a solution made up of 20 mL of 0.5 M solution of acetic acid and 10 mL of 0.5 M sodium acetate? c) If 10 mL of 0.1 M NaOH is added to the solution in part b, what is the final pH? d) What is the pH of a solution containing equal concentrations of acetic acid and sodium acetate?
a. Calculate the pH of 0.250 L of a 0.36 M formic acid-0.30 M sodium formate buffer. Express your answer using three significant figures.   b. After the addition of 0.0050 mol of NaOH. Assume that the volume remains constant. Express your answer using three significant figures.   c. After the addition of 0.0050 mol of HCl. Assume that the volume remains constant. Express your answer using three significant figures.
The pKa of acetic acid CH3COOH is 4.76. A buffer solution contains CH3COOH and CH3COONa and has a pH of 4.76 and a total acetate concentration (acid and base forms) of 0.400 M. What is the concentration of CH3COOH?
If the pKa of HCHO2 is 3.74 and the pH of an HCHO 2/NaCHO2 solution is 3.89, which of the following is true? A) [HCHO2] < [NaCHO2] B) [HCHO2] > [NaCHO2] C) [HCHO2] = [NaCHO2] D) [HCHO2] >> [NaCHO2] E) It is not possible to make a buffer of this pH from HCHO 2 and NaCHO2
Calculate the pH of a solution that is 0.27 M in HF and 0.11 M in NaF. Express your answer using two decimal places.
Ammonium (NH4+) is a weak acid with a pK a of 9.26. The dissociation is:NH4+ ⇌ NH3 + H+Calculate the mass of ammonium added to 1 L of water in order to obtain a pH of 4 at equilibrium. 
Which of the following are valid ways to make an ammonia/ammonium buffer for use in a laboratory? Explain your choices. A) mix equal volumes of 1 M NH3 and 1 M NH4+  B) Mix equal volumes of 1 M NH3 and 0.01 M NH4+  C) Mix equal volumes of 1 M NH3 and 1 M HCl D) Mix some volume of 1 M NH3 and half as much HCl
Which solution would come closest to making a pH 7 buffer? (Reference data for phosphoric acid, H3PO4: pKa1 = 2.2, pKa2 = 7.2, pKa3 = 12.2) a. a solution containing equal amounts of Na2HPO4 and Na3PO4 b. a solution containing equal amounts of H3PO4 and NaH2PO4 c. a solution containing equal amounts of NaH2PO4 and Na2HPO4 d. a solution of Na2HPO4 e. a solution of NaH2PO4    
Benzoic acid C6H5COOH is a weak acid with K a = 6.3 x 10-5 C6H5CO2H (aq) + H2O (l) ⇌ H3O+ (aq) + C6H5CO2- (aq) a) Calculate the pH of a 0.150 M benzoic acid solution. Show all calulations. b) Suppose 1.44g of sodium benzoate, Na+C6H5COO-, is added to 100.0 mL of the 0.150 M benzioic acid solution. Calculate the pH of the resulting buffer solution assuming the volume of the solution does not change on addition of the solid.
You need to produce a buffer solution that has a pH of 5.21. You already have a solution that contains 10. mmol (millimoles) of acetic acid. How many millimoles of acetate (the conjugate base of acetic acid) will you need to add to this solution? The pKa of acetic acid is 4.74. Express your answer numerically in millimoles.
Calculate the pH of a buffer solution that is 0.60 M in NH4Cl and 0.75 M in NH3. (K b = 1.8 × 10−5 for NH3) a. 9.16 b. 11.60 c. 9.35 d. 4.84  
An equal volume mixture of which two solutions will produce a buffer solution? a. 1 M HClO4 and 1 M KClO4 b. 2 M HC2H3O2 and 1 M KOH c. 1 M NH3 and 1 M HCl d. 1 M HF and 2 M NaOH  
The pKa of formic acid (HCOOH) is 3.74, a monoprotic weak acid. A 1.0 L sample of a buffer with a pH of 4.5 is combined with 0.09 moles of NaOH. What is the new pH of the solution? The ratio of HCOO- to HCOOH is 0.86 M to 0.15 M.
Which of the following solutions is a good buffer system?a. 0.10M LiC2H3O2 and 0.10M HBrb. 0.10 M NH4+ and 0.10M HIc. 0.10 M LiOH and 0.10M KOHd. 0.10M HC2H3O2 and 0.10M LiC2H3O2
You are asked to prepare a pH = 4 buffer starting from 1.50L of .02 M solution of benzoic acid and an excess of sodium benzoate. a. What is the pH of the benzoic acid solution prior to adding sodium benzoate? b. How many grams of sodium benzoate should be added to prepare the buffer? Neglect the small volume change that occurs when the sodium benzoate is added.
Calculate the pH of a solution that is 0.230 M in benzoic acid and 0.130 M in sodium benzoate. a salt whose anion is the conjugate base of benzoic acid.
Calculate the pH of a solution that is 0.170 M in benzoic acid and 0.190 M in sodium benzoate, a salt whose anion is the conjugate base of benzoic acid.
What is the ratio of acetate ion to acetic acid (Ka = 1.76 times 10-5) in a buffer containing these compounds at pH 4.560?
Calculate the ratio of CH3NH2 to CH3NH3Cl required to create a buffer with pH = 10.28. Express your answer using two significant figures. 
What is the pH change of a 0, 210 M solution of Citric acid (pKa = 4.77) if citrate is added to a concentration of 0.125 M with no change in volume?
If a buffer solution is 0.140 M in a weak acid (K_a = 8.1 times 10^-5) and 0.450 M in its conjugate base, what is the pH?
What is the pH of 1.00 L of a buffer that is 120 M nitrous acid (HNO2) and 0.170 M NaNO2? pKa of HNO2 = 3.40
The Ka of nitrous acid, HNO2, is 4.5x10-4. What [NO2-]/[HNO2] ratio is necessary to make a buffer with a pH of 3.71?
Determine the pH change when 0.091 mol KOH is added to 1.00 L of a buffer solution that is 0.324 M in HNO2 and 0.297 M in NO2-. pH after addition - pH before addition = pH change =
A buffer solution made from HCIO and NaCIO has a pH of 7.20.If pKa for HCIO is 7.46, what is the [CIO-]/[HCIO] in the buffer? 
What is the ratio of acetate ion to acetic acid (K a = 1.76 x 10 -5) in a buffer containing these compounds at pH 4.570? 
Write the Henderson-Hasselbalch equation for a propanoic acid solution (CH3CH2CO2H, pKa = 4.874) using the symbols HA and A-, and the given pKa value for propanoic acid in the expression. pH = pKa + log [A-] / [HA]Using the equation above, calculate the quotient [A-] / [HA] at pH 4.112. pH 4.874. pH 5.115.
If a buffer solution is 0.220 M in a weak base (K b 8.6 x 10-5) and 0.590 M in its conjugate acid, what is the pH? 
You need to prepare 100.0 mL of a pH=4.00 buffer solution using 0.100 M benzoic acid (pKa = 4.20) and 0.160 M sodium benzoate. How much of each solution should be mixed to prepare this buffer?
A buffer solution is prepared by adding 0.121 mol of ammonium chloride to 5.00 times 10^2 mL of 0.544 M solution of ammonia. What is the pH of the buffer? Ka = 5.6 times 10^-10 A buffer solution is prepared by adding 0.121 mol of ammonium chloride to 5.00 times 10^2 mL of 0.544 M solution of ammonia. If 0.0110 mol of NCI gas is bubbled into 5.00 times 10^2 mL of the buffer, what is the new pH of the solution? Ka = 5.6 times 10^-10
Calculate the pH of a solution that is 0.220 mol L-1 in nitrous acid (HNO2) and 0.300 mol L-1 in potassium nitrite (KNO2). The acid dissociation constant of nitrous acid is 4.50x10-4. 12.820, 3.481, 4.527, 10.519, 3.212
A buffer solution is made using a weak acid, HA, that has a pK a of 6. If the pH of the buffer is 8, what is the ratio of A- to HA?
Which one of the following pairs  cannot be mixed together to form a buffer solution?
What is the final pH when 42.1 mL of 3.2 M NaOH is added to 1.00 L of 0.150 M HF (Ka = 3.5 x 10 -4)
A buffer solution is 0.280 M in a weak base (K b = 3.5 x 10 -5) and 0.550 M in its conjugate acid, what is the pH?
500.0 mL of 0.110 M NaOH is added to 575 mL of 0.200 M weak acid (K   a = 7.16 x 10-6). What is the pH of the resulting buffer? HA (aq) + OH - (aq) → H2O (l) + A- (aq) 
You need to prepare 100.0 mL of a pH=4.00 buffer solution using 0.100 M benzoic acid (pKa = 4.20) and 0.140 M sodium benzoate. How much of each solution should be mixed to prepare this buffer?
A buffer solution is made using a weak acid. HA, that has a pKa of 5. If the pH of the buffler is 6, what is the ratio of A- to HA? 
Which pair of compounds act as a buffer in aqueous solution?a. H3PO4 (phosphoric acid) and H2PO4- (dihydrogen phosphate ion)b. NaCN (sodium cyanide) and KOH (potassium hydroxide)c. HCIO4 (perchloric acid) and NaOH (sodium hydroxide) 
You need to prepare 100.0 mL of a pH = 4.00 buffer solution using 0.100 M benzoic acid (pKa = 4.20) and 0.180 M sodium benzoate. How much of each solution should be mixed to prepare this buffer?
A buffer solution contains 0.323 M KHSO3, and 0.257 M K2SO3.If 0.0495 moles of sodium hydroxide are added to 250. mL of this buffer, what is the pH of the resulting solution?(Assume that the volume does not change upon adding sodium hydroxide)pH =
What is the pH of a solution containing 0.015 M CH3CH(OH)COOH and 0.018 M CH3CH(OH)COO (made by dissolving CH_3 CH(OH)COONa)? The Ka for CH3CH(OH)COOH is 0.000839
Use the Henderson-Hasselbalch equation to calculate the pH of each solution: A solution that is 0.15 Min HCHO2 and 0.15 Min NaCHO2 Express your answer using two decimal places.